DE102008001000B4 - Layer system for electrodes - Google Patents

Abstract

Layer system for electrodes, consisting of a piezoelectric substrate with or embedded in the substrate strip structures of a composite material, which consists of a metallic matrix material having at least one storage phase of carbon nanostructures.

Description

The This invention relates to the field of materials science and relates to a layer system for Electrodes, in particular for Interdigital transducer for surface acoustic wave devices, and especially for Interdigital transducer for surface acoustic wave devices, which, for example, as a frequency filter, sensors or actuators can be used but also for electrodes from other micro-electro-mechanical systems.

acoustic Surface wave components (Surface Acoustic wave (SAW) components) generally consist of a piezoelectric substrate or a piezoelectric thin film a non-piezoelectric substrate and one or more Interdigital transducers (IDT) for coupling and decoupling the electrical Energy, as well as from corresponding contact areas (pads).

at the operation of the surface acoustic wave devices at high temperatures and / or high SAW power may cause it to be stress-induced precipitate for SAW components due to migration effects (akustomigration), to flaking (failure of the interface metal layer substrate) or to cracking in the substrate itself. All this limits the Power compatibility, the reliability, as well as the lifetime of the components.

One Another problem with SAW components is the contact the IDT, for what adherent connections between a contact element (eg. or Au wire) and the pads must be realized. For components with operating frequencies in the GHz range, these pads must also be correspondingly be thickened (increase the layer thickness of the metallization in the pad area).

Interdigital transducer for SAW components often either from Al-based or Cu-based thin-film systems (metallization) with typical dimensions of a total thickness of 50 to 500 nm with or without adhesive layer (usually Ti) produced. Usual separation methods are Electron beam evaporation or magnetron sputtering. These thin-film systems be either as a single layer or as alloys or as multilayer systems deposited. The structuring of the metallization layers takes place either over Lift-off technique or via etching techniques with the help of a mask. Due to a given relationship between Migration and the mechanical properties of metallization can the power compatibility and consequently the lifetime of the SAW devices through improved thermomechanical Properties of the metallization can be increased.

Metal matrix composite materials embedded carbon nanotubes (CNT-MMC) have been in shape in recent years Of compact powder materials have become known, the special investigated CNT-Cu sintered materials markedly improved mechanical Have properties.

such But materials are due to their structure as well as their powder metallurgical Do not manufacture for Metallizations for the manufacture of SAW devices suitable, which with thin-film techniques and with finger widths of the interdigital transducers down to the sub-micron range must be made.

Next, electrochemical methods are known for the production of metallic thin films, such as. As Cu, Ni, Ag, or the like. In particular, a process for the electrochemical deposition of CNT-Cu composites ( US 2007/0199826 A1 . US 2007/0158619 A1 . US 7226531 B2 ) known. It has been shown in principle that after functionalization of the CNTs by means of chemical methods, CNT-Cu composite layers can be produced on substrates having improved mechanical and tribological properties by means of electroplating.

After US Pat. No. 6,709,562 B1 is a method for the production of buried in an insulator interconnects for microelectronic circuits known.

Next is after US 7226531 B2 the production of a connecting wire ("interconnection wire") made of a composite material of CNTs and metal on flexible substrates known.

Known is also that nanostructures and especially carbon nanotubes, extraordinary properties can have [Dresselhaus, M.S., Dresselhaus, G., Avouris, P. (Eds.): Carbon Nanotubes, Synthesis, Structure, Properties, and Applications. Springer-V. Berlin (2001)].

It is still known after the WO 2006/133466 A1 an arrangement for pressure measurement, in particular in the case of gas-filled tires, in which a surface wave sensor with excitation and reception electrode is arranged on a carrier substrate which comprises a nanocrystalline carbon, preferably carbon fullerenes, carbon nanofibers or carbon nanotubes, and the surface acoustic wave Sensor is connected to a surface on which pressure is applied.

Also known is the US 2003/0210111 A1 a surface acoustic wave filter and a method for its production. In doing so, Koh nenstoffnanoröhren used as a transmission medium for the acoustic waves.

disadvantage the known solutions for metallizations for interdigital transducers for SAW components exist above all in the not yet sufficient power stability and lifetime in terms of acoustomigration and mechanical Chipping or failure of the interface between metallization and substrate, in particular for Power filters, optical applications and for actuators.

The The object of the present invention is to specify a layer system for electrodes with improved power compatibility and lifetime.

Is solved the object by the invention specified in the claims. Advantageous embodiments are the subject of the dependent claims.

The Layer system according to the invention for electrodes consists of a piezoelectric substrate with it or substrate-embedded strip structures made of a composite material, which consists of a metallic matrix material with at least one Einlagerungsphase consists of carbon nanostructures.

advantageously, is the layer system for interdigital transducers for acoustic Surface Acoustic Wave Components used.

Farther Advantageously, the composite material has amorphous or nanocrystalline Structure on.

Also As a metallic matrix material, it is a high fcc material conductivity available.

And Also advantageously, as metallic matrix material Al, Cu, Ag, Au, Pt or Ru present.

It is also advantageous if the metallic matrix material to 50.1 to 99.9% by volume is included.

And It is also advantageous if the intercalation phase consists of carbon nanotubes, carbon nanowires, fullerenes or graphene, and more advantageously the carbon nanotubes are single-walled (Single wall CNT) or multi-walled (multiwall CNT) are formed, and / or the storage phase in a directed arrangement in the matrix material is contained and / or as Einlagerungsphase completely filled carbon nanotubes or filled fullerenes are present or a combination of such and / or as Einlagerungsphase one Combination of filled Carbon nanotubes or filled Fullerenes with unfilled ones Carbon nanotubes or unfilled Fullerenes or graphenes are present or combination of such.

Advantageous it is also when the carbon nanostructures by catalytic CVD method produced Are carbon nanostructures.

From It is also an advantage if in addition to the storage phase further globular, tubular, rod-shaped or area Structures are contained in the matrix material.

And It is also advantageous if the carbon nanostructures of the Storage phase cohesively and / or non-positively connected to the substrate. being still advantageously directed arranged carbon nanostructures of the storage phase all connected with one end to the substrate cohesively and / or non-positively are.

Also It is advantageous if between substrate and layer system one Buffer layer is present.

Farther it is advantageous if on the layer system, a cover layer is applied.

And It is also advantageous if the strip structures are complete or almost complete embedded in the substrate.

at the method according to the invention for producing a layer system for electrodes are either on a substrate layer on a substrate particle or applied a layer of a catalyst material, this layer composite becomes a temperature increase exposed and subsequently by means of plasma-assisted processes carbon nanostructures produced, and subsequently at least the spaces between the Carbon nanostructures through a metallic matrix material filled out and / or on a substrate with or without layers already thereon by means of plasma-assisted Method particles are applied during or after application lead to the formation of carbon nanostructures and below the spaces between the carbon nanostructures through a metallic matrix material filled out become.

advantageously, is used as a seed layer material Cu or Ru or TaN.

Further advantageously, as Ka used as catalyst material Fe, Ni and / or Co.

And also advantageously be used as filling material for the carbon nanotubes Fe, Ni and / or Co are used.

Also Advantageously, a barrier layer is formed between the substrate and the seed layer applied.

It is also advantageous if CH ₄ gas is used in the plasma-assisted process, wherein advantageously a further gas is used for diluting the C content, which is advantageously used as Ar or He.

From It is also advantageous if, as metallic matrix material, Al, Cu, Ag or Au are used or alloys or multilayers the same.

Also it is advantageous if the nanostructures with an intermediate layer which are preferably applied by means of atomic layer deposition (ALD) is, where advantageously the intermediate layer of a metal or an oxide or nitride such as Ru, Ta, Ti, TaN, TiN, Hf oxide or Zr oxide or multilayers or alloys thereof, and as such is used.

With the solution according to the invention it possible for the first time a composite material as a material for electrodes and in particular for the Finger electrodes of the interdigital transducers of surface acoustic wave devices to use. The use of composite materials based on a Metal or a metal alloy or metal multilayers in Connection with nanostructures as storage phase as thin-film systems as material for Finger electrodes of the interdigital transducer is not yet known. In particular, it is not known to use carbon nanostructured metal matrix composites and in particular carbon nanostructured Cu or Al composites.

From of particular interest in connection with nanocomposite layers for the o. G. Applications as a layer system for interdigital transducers for acoustic Surface Acoustic Wave Components are strictly ordered 0-, 1- or 2-dimensional carbon nanostructures, like fullerenes, single-walled or multi-walled carbon nanotubes (carbon Nanotubes = CNTs) or carbon nanowires or graphenes. CNTs can with different quality than single-wall CNT = SWCNT) or multi-walled (multiwall CNT = MWCNT) carbon nanotubes either via laser arc, Arc process or CVD produced with or without plasma support become. Especially the so-called catalytic CVD (cCVD method) is for the production of larger amounts of CNT suitable. The properties of the produced CNTs are dependent on Production method. about cCVD manufactured CNTs are predominant MWCNTs in the diameter range between 10 nm and 100 nm. The outer sheaths have usually many structural defects or they are partially or completely amorphous. Also can the CNTs are purified, functionalized or during or after production be filled with different materials.

defect-free CNTs can an extremely high Young's Modulus (up to about 1.2 TPa) and a ballistic electron transport as well as a high heat conduction exhibit.

With the solution according to the invention for layer systems for interdigital transducers for surface acoustic wave devices can the previous disadvantages of the known solutions for interdigital transducers for SAW components be corrected or at least significantly improved, in particular the homogeneous distribution of CNTs within the layer system according to the invention improved and their arrangement can be controlled specifically.

Farther can the viscosity of the layer material can be adjusted in a certain range and / or be kept at a certain value, whereby the insertion loss of Component can be positively influenced.

According to the invention can Manufacturing performance-friendly Metallizations for Electrodes and in particular for Interdigital transducer for SAW components Layer systems with at least one intercalation phase (composite layer system) zero (fullerenes), single (carbon nanotubes, carbon nanowires), or two-dimensional (graphene) carbon nanostructures are used, those using a thin-film deposition process (preferably electrochemical deposition (electroplating)) produced can be. to improved wetting with the matrix material, the CNTs are functionalized or provided with at least one intermediate layer after growth on the carbon modifications, preferably with atomic layer Deposition (ALD), be applied.

The coating systems according to the invention for electrodes and in particular for interdigital transducers for surface acoustic wave components can be produced, for example, by applying catalyst particles (for example Fe, Ni, Co or others) to a substrate. This is preferably done in a continuous system, either directly the catalyst particles, z. B. over a sputtering technique, are applied from a supersaturated vapor, or in a continuous system, first a thin layer (1-5 nm thickness) of the Ka is deposited on one of the thin-film techniques (sputtering, evaporation, CVD) on the surface of the substrate and is carried out via a subsequent heat treatment, the formation of the catalyst particles by agglomeration effects. The particle size is preferably between 5 and 30 nm, depending on the process parameters.

following For example, the coated substrate is thermally exposed in a C-containing atmosphere activated processes or thermal-plasma-activated processes with Carbon nanostructures, e.g. As carbon nanotubes coated. These carbon nanotubes have in this case a preferred direction with respect to the surface of the Substrate.

In a subsequent Process the carbon nanostructures are functionalized (formation of O-H groups) and / or over ALD with at least one primer layer (eg TaN or Ru) coated, and subsequently by means of a deposition process (preferably electroplating) with the coated metallic matrix material, so that the spaces between partially or completely filled in the carbon nanostructures, and the matrix material as a cladding for the carbon nanostructures serves. Thus, a composite layer is obtained, the aligned Contains carbon nanostructures in a matrix material the carbon nanostructures embedded in a length or over a thickness are at least equal to the thickness of the layer. Furthermore is an undirected incorporation of the carbon nanostructures possible in the matrix material, when the carbon nanostructures together with the metal layer be deposited. For this purpose, advantageously, the carbon nanostructures the Electrolytes for the electrochemical deposition is added.

Farther Is it possible, to combine both manufacturing processes, so that the layer system Contains areas of directionally arranged carbon nanostructures and simultaneously other areas where the carbon nanostructures are undirected are arranged.

It is possible, too, Areas of the layered system with directional and / or non-directional To combine storage phases with areas without storage phase.

Next electroplating may involve the application of at least the matrix layer also over other methods, for example, electroless electroless plating respectively.

Farther it is possible to coat a substrate with the layer system according to the invention and subsequently removing the substrate.

The Layer systems according to the invention can also for Electrodes for Micromirror systems, for microelectromechanical pressure sensors or actuators, for piezoelectromechanical Controls are used and there also shows an improved power compatibility and lifetime.

following the invention is based on an embodiment explained in more detail.

there demonstrate

1 a schematic representation of the layer system according to the invention in cross section with arranged arranged carbon nanostructures in the form of carbon nanotubes
and

2 a schematic representation of the layer system according to the invention in cross section with undirected arranged carbon nanostructures in the form of carbon nanotubes
and

• a) CNT-Cu-Schichtsystem mit einer Schichtdicke von 1,95 μm,
• b) mit einem dünnen Ta(N)-Schicht mittels ALD beschichtete CNT vor dem Cu-Elektroplating

3 Examples of transmission electron microscopic images

• a) CNT-Cu layer system with a layer thickness of 1.95 μm,
• b) with a thin Ta (N) layer using ALD coated CNT before Cu electroplating

example 1

The Production of the interdigital transducer for SAW components from the layer system according to the invention is shown using the Damascus technique as an example.

A quartz wafer provided with a resist mask is patterned by means of reactive ion etching into finger-shaped arrangements, the interdigital transducers, of dimensions (finger widths) of 3.76 μm, and the remaining lacquer is peeled off. Subsequently, this structured arrangement is provided with a 5 nm thick layer of TaN as a barrier layer and subsequently with a 50 nm thick Cu layer as a seed layer. These layers are sputtered on. Thereafter, on the Cu layer, Ni catalyst particles of an average size of 20 nm having a density of 1000-5000 particles / μm ^{3 are} deposited by a supersaturated vapor sputtering method.

In the following plasma-assisted CVD process in the temperature range between 300 ° C and 500 ° C using CH ₄ mono- and multi-walled carbon nanotubes grow with a average length of 1-3 microns.

Subsequently, over Elektroplating Cu using sulfuric acid electrolyte on the surface and around the carbon nanotubes deposited so that the array of CNTs is completely covered. By chemical-mechanical polishing (CMP) with a standard Cu suspension becomes the resulting layer system structured. This results in buried interdigital transducer finger structures from a CNT-Cu layer with substantially unidirectionally embedded CNT's received.

at a layer thickness of 1.95 microns the CNT-Cu layer is the electrical resistance is 1.73 μOhmcm.

These Interdigital transducers show a significantly higher power compatibility and lifetime compared to Cu layers without CNT aging phases.

Example 2

A lacquer-masked wafer of LiNbO ₃ is patterned by means of reactive ion etching into finger-shaped arrangements of 0.5 μm width and a similar distance (interdigital transducer for filter structures in the GHz range) and the residual lacquer is peeled off. Subsequently, this structured arrangement is provided with a 3 nm thick layer of Ta-Si-N as a barrier layer and subsequently with a 50 nm thick Cu layer as a seed layer. These layers are sputtered on. Thereafter, chemically functionalized carbon nanotubes with a narrow diameter distribution with a maximum at 20 nm diameter and a length between 3 and 5 microns are placed in a Cu electrolyte and circulated the bath. In a further process step, the coating with the Cu electrolyte takes place via electroplating.

These Interdigital transducers also show a significantly higher power compatibility and lifetime compared to Cu layers without CNT aging phases.

1

substratum

2

interlayer

3

seed layer

4

interstitial phase

5

metallic matrix material

Claims (29)

Layer system for electrodes, consisting of a piezoelectric substrate with it or in the substrate embedded strip structures of a composite material, which from a metallic matrix material with at least one storage phase consists of carbon nanostructures. Layer system according to claim 1, wherein the layer system for interdigital transducers for surface acoustic wave devices is used. Layer system according to claim 1, wherein the composite material has amorphous or nanocrystalline structure. Layer system according to claim 1, in which as metallic Matrix material a fcc material with a high conductivity is available. Layer system according to claim 4, in which as metallic Matrix material Al, Cu, Ag, Au, Pt or Ru is present. Layer system according to claim 1, wherein the metallic Matrix material is contained at 50.1 to 99.9 vol .-%. Layer system according to claim 1, wherein the storage phase from carbon nanotubes, carbon nanowires, fullerenes or graphene. Layer system according to claim 7, wherein the carbon nanotubes are single-walled (Singlewall CNT) or multi-walled (multiwall CNT) are formed. Layer system according to claim 7, wherein the storage phase is contained in a directional arrangement in the matrix material. Layer system according to Claim 7, in which the storage phase Completely filled Carbon nanotubes or filled Fullerenes are present or a combination of such. Layer system according to Claim 7, in which the storage phase a combination of filled carbon nanotubes or filled Fullerenes with unfilled ones Carbon nanotubes or unfilled fullerenes or graphenes are present or combination of such. Layer system according to claim 1, wherein the carbon nanostructures carbon nanostructures made by catalytic CVD processes are. Layer system according to claim 1, wherein in addition to the Storage phase further globular, tubular, rod-shaped or area Structures are contained in the matrix material. Layer system according to claim 1, wherein the carbon nanostructures the storage phase cohesively and / or non-positively connected to the substrate. The layer system of claim 14, wherein directed arranged carbon nanostructures of the storage phase all connected with one end to the substrate cohesively and / or non-positively are. Layer system according to claim 1, wherein between Substrate and layer system a barrier layer is present. Layer system according to claim 1, wherein on the layer system a cover layer is applied. Layer system according to claim 1, wherein the strip structures Completely or almost completely embedded in the substrate. Method for producing a layer system for electrodes according to one of the claims 1 to 18, in which either on a substrate located on a Seed layer particles or a layer of a catalyst material applied, this layer composite exposed to a temperature increase and subsequently by means of plasma-assisted processes carbon nanostructures be prepared, and subsequently at least the spaces between the carbon nanostructures through a metallic matrix material filled out and / or on a substrate with or without it already layers applied by means of plasma-assisted processes particles be that while or after application to the formation of carbon nanostructures lead and below the spaces between the carbon nanostructures through a metallic matrix material filled out become. The method of claim 19, wherein as a seed layer material Cu or Ru or TaN is used. The method of claim 19, wherein as the catalyst material Fe, Ni and / or Co are used. A method according to claim 19, wherein as filler material for the Carbon nanotubes Fe, Ni and / or Co are used. The method of claim 19, wherein between substrate and seed layer, a barrier layer is applied. The method of claim 19, wherein in the plasma-enhanced method CH ₄ gas is used. The method of claim 24, wherein another Gas for dilution the C content used becomes. The method of claim 25, wherein Ar or He is used becomes. The method of claim 19, wherein as metallic Matrix material Al, Cu, Ag or Au are used or alloys or multilayers of the same. The method of claim 19, wherein the nanostructures are provided with an intermediate layer, preferably by means of Atomic Layer Deposition (ALD) is applied. A method according to claim 28, wherein as an intermediate layer a metal or an oxide or nitride, such as Ru, Ta, Ti, TaN, TiN, Hf oxide or Zr oxide or multilayers or alloys thereof be used.